The invention relates to a compound needle for knitting, warp knitting or hosiery machines, comprising: a needle part with a needle shaft and a needle hook, the needle shaft having a front side with a slot-shaped recess, a rear side, a longitudinal direction and a guide channel extending in the longitudinal direction, and a slide part with a slide shaft, which is insertable into the guide channel and is moveable to and fro in the latter, and with a slide hook which is open in the opposite direction to the needle hook, the slide hook being insertable at least partially into the recess in order to take over a stitch located on the needle shaft. The invention also relates to a knitting machine of any kind and being provided with compound needles mentioned above.
When using a hook-type needle, the thread is placed over the needle shaft by means of a first sinker as a loop, i.e. sunk, and then is inserted into the needle hook. Thereafter, the needle hook is closed by means of a pressing element and the old stitch, which is still located on the needle shaft, is pressed over the needle hook, i.e. knocked over. In contrast to the advantage of a regular and clean stitch formation there are also various disadvantages. These reside in the fact that, in order to open and close the needle hook, additional and controllable elements are required, for which reason a lot of space is necessary, the machines can only be provided with a small number of systems and the achievable outputs and the pattern options are low.
The predominant use nowadays of latch-type needles makes possible an automatic closing and opening of the hooks in contrast due to the pivotably mounted latches so that additional elements are not required for this purpose. The use of latch-type needles offers the advantages in addition of a low spatial requirement and also the possibility resulting therefrom of a large system number and achievable high output. Finally, when using latch-type needles, patterns which cannot be produced with hook-type needles can be produced, such as numerous different machine types demonstrate (e.g. right/left, right/right and left/left machines). A not unsubstantial disadvantage of latch-type needles exists however in the fact that the beginning of a knitting process cannot be automated because the automatic process of the latch opening makes it a precondition that stitches are already located in the needle hooks. It is therefore necessary to open the needle latches manually at the beginning of each knitting process, which is laborious and time-consuming.
This disadvantage can be avoided by using two-part compound needles, described subsequently as xe2x80x9cnormalxe2x80x9d, in which the hooks are opened and closed by means of a moveable slide which is controllable by means of needle cams. In addition, the advantage is given relative to latch-type needles that there are no pivotable parts which can become worn with high operating speeds or can be destroyed by breakage. However against these advantages there are disadvantages, in that the insertion of the threads into the needle hooks is problematic and it cannot be reliably avoided when using double-bed knitting machines (for example circular knitting machines with needle cylinders and dials) that faults are produced in the stitch formation. Normal compound needles have therefore only been partly successful in the case of circular knitting machines and also only with right/left machines. In contrast, compound needles of this type have been used widely with warp knitting machines because the threads can be inserted here by means of the eye needles securely into the needle hooks and hence the controlled movements of the slides can be fully exploited.
A further type of stitch formation, which has not yet been applied to date in practice, starts from a two-part needle of the type described initially (U.S. Pat. No. 1,385,929 and U.S. Pat. No. Re. 15,741). This needle, which is described subsequently as xe2x80x9cmodifiedxe2x80x9d compound needle, differs as do other comparable needles of this type from the above-mentioned normal compound needle in that its slide part has a catch or securing hook, which is described subsequently as xe2x80x9cslide hookxe2x80x9d and essentially is disposed mirror-symmetrically to the needle hook of the associated needle part, i.e. is opened towards the front side of the needle part. The stitch formation is effected here in that a stitch, which is suspended on the shaft of the needle part and produced in a preceding stitch formation process, is caught by the slide hook and is secured whilst the needle part is simultaneously withdrawn in order to pull a thread placed in the needle hook through the xe2x80x9coldxe2x80x9d stitch retained by the slide hook so as to form a loop. In the further course, the slide hook is then firstly raised somewhat in order to release the old stitch, whereupon the needle part is also raised in order that, on the one hand, the newly formed loop or stitch slides onto its shaft and, on the other hand, the needle hook can take up a further thread. A needle of this type has like a normal compound needle the advantage that it enables an automatic commencement of the knitting process. In contrast to a normal compound needle, the modified compound needle is suited above all for machines with two knitting beds because the old stitch can always be retained in the slide hook until the new thread loop has slipped securely into the needle hook.
One problem occurring during tests on the modified compound needle resides in the fact that the slide hook does not always reliably take over the old stitch suspended on the shaft of the needle part. Especially when using hairy yarns and filament yarns, it was observed that the slide hook only takes over the old stitch in part and double stitches are formed. When knitting small stitches, faults are produced moreover in that the needle hook becomes partly stuck in the thread of the old stitch retained by the slide hook. Thus the modified compound needles to date cannot be used in general despite their advantages to replace hook-type needles, latch-type needles or normal compound needles, in particular if knitted articles are to be produced which have small dense stitches. Practical applications of the modified compound needles have therefore not become known to date.
One main reason for the portrayed disadvantages seems to reside in the fact that, in the needles of this type which have become known to date, the shanks of the newly formed stitch retained by the slide hook, at least at the very moment in which the needle hook carrying the new thread is intended to be moved through the old stitch, are situated very closely next to each other because of the selected needle construction and hence the intermediate space between the stitch shanks cannot be readily passed by the needle hook. This difficulty is increased even more by the vibrations which are unavoidable during operation of a knitting or hosiery machine. Also the control of the slide part on the needle part by means of a tongue and groove connection and a collar spring encompassing the slide parts at the external circumference do not contribute to improving the stitch formation. Finally, the known needle construction demands additional machining of the slide hook in order that the latter enters reliably into a recess configured in the needle shaft upon takeover of the old stitch, as a result of which sharp corners and edges are formed which can damage the sensitive thread material.
With this background in mind it is an object of this invention to design the compound needle specified above such that the needle hook can enter reliably into the old stitch under all conditions which may come across in practice during normal knitting.
A further object of this invention is to design the compound needle specified above such that the risk of damage to the old stitches or to the threads forming the stitches is extensively avoided.
Yet another object of the invention is to provide a needle of the type described above which is suitable also for producing a clean and uniform stitch structure even during production of small and tight stitches and also when using critical yarns, such as for example hairy yarns or filament yarns, without the threads which are used being torn or being cut through.
Further, it is also an object of this invention to suggest a knitting machine being provided with compound needles according to this invention.
These and other objects are solved by a compound needle of the type specified above which is characterized in that the guide channel has a cover bridging the slide shaft at least on a part of its length and in that the thickness of the slide hook is greater at least in a spread portion taking over the stitch and keeping it wide than the width of the guide channel, and/or the thickness of the needle hook is smaller than the thickness of the needle shaft, and further in that a knitting machine is provided with such compound needles.
The invention offers on the one hand the advantage that the slide part is mounted displaceably on the needle part in a manner which has proved its worth in the case of normal compound needles and which also ensures in the case of the modified compound needles according to the invention that the slide part is guided reliably and with narrow tolerances on the needle part during operation of a knitting or hosiery machine in all occurring conditions, in particular with the normal temperature increases. Consequently, any relative movements between the needle part and the slide part which are radial and effected perpendicularly to the longitudinal direction and are detrimental to a clean guidance of the needle hook through the old stitch, are extensively eliminated. On the other hand, compensation is made according to the invention for the comparatively small thickness of the slide shaft, conditioned in principle by the narrow guide, at that point at which the stitch formation takes place, in that either the slide hook is selected to be thicker than corresponds to the guide groove in the needle part, or the thickness of the needle hook relative to the needle shaft is reduced and consequently is approximately the width of the guide channel. In this manner, the spacing of the stitch legs at the moment at which the old stitch is passed by the needle hook is spread sufficiently widely and consequently it can be avoided in conjunction with the reliable guidance of the slide part on the needle part that the needle hook or its free tip is inserted into the stitch shanks and damages these or even forms double stitches. One particular advantage of the needle construction according to the invention resides finally in the fact that neither individual portions of the slide shaft or of the slide hook nor individual portions of the needle hook need be machined in such a manner which leads to sharp edges or the like and hence to damage of the sensitive yams during the stitch formation process.
Further advantageous features of the invention are produced from the sub-claims.